Los Angeles Says Goodbye to Iconic Sixth Street Bridge

Anyone who has seen the movie "Grease" will recall the famous drag race scene. If you wondered where it was filmed, that would be the historic Sixth Street Viaduct in Los Angeles. This location was home to numerous movies, TV shows and music videos and a gateway to downtown L.A. This towering concrete icon spanned the Los Angeles River, the Santa Ana Freeway (U.S. 101), several local streets and 18 active railroad tracks.

Millions of dollars were spent to repair and maintain the crossing over the years. Since its construction in 1932, the 3,500-foot-long and 60-foot-tall viaduct's 50,000 cubic yards of concrete continued to deteriorate due to an alkali-silica reactivity (ASR) condition. ASR is a chemical reaction that occurs between the alkalis in the cement and a reactive form of silica in the aggregate. This reaction forms a gel, which expands and produces cracks in the concrete when exposed to moisture. Of the dozen or so historic pre-World War II bridges that span the Los Angeles River, this is the only one to suffer from ASR.

Replace vs. Renovate

Ultimately, a decision was made to replace the bridge since it would be too costly to properly bring it to code. Funded by a combination of federal, state and city dollars, the Skanska-Stacy and Witbeck Joint Venture, (SSW-JV) was chosen as the construction manager/general contractor to replace the Sixth Street Viaduct. As a subcontractor to SSW, Silverado Contractors Inc. was selected to demolish the entire structure and make way for a new viaduct. Silverado is a union contractor providing a full spectrum of demolition and excavation services to private developers, general contractors, industrial and public works clients across the West Coast.

According to Silverado Estimator Dan Ngo, "Our scope of expertise involves every conceivable type of project including building demolition, selective demolition, industrial, marine, transportation, bridge removal, remediation, complete site decommissioning, plant closure, asset recovery and recycling, excavation and site preparation." Other Silverado projects include the dismantling of the San Francisco Oakland Bay Bridge from Yerba Buena Island to Oakland, the Carquinez Bridge and I-80 at Crockett Interchange in Crockett/Vallejo, California, and the Maxwell Bridge in Napa, California.

Conducting the "˜Slow Jam'

Demolition of the Sixth Street Bridge was planned, orchestrated and executed by Silverado's onsite team of 20 professionals, beginning in early February 2016. Several segments of the viaduct demolition were limited to specific time constraints. Dubbed "Slow Jam" by Los Angeles' Mayor Eric Garcetti, the project began with the removal of four spans over the U.S. 101 freeway during a 36-hour weekend shutdown.

As Silverado's crews continued viaduct demolition working from the east to west ends, various removal methods were implemented to ensure streets, sidewalks, and adjacent buildings were not damaged, recalls Ngo.

"The Silverado team was ready for the challenge and crews installed a vertical debris shield of chain-link fence material to prevent concrete debris from damaging adjacent unreinforced brick buildings. Bridge girders and columns weighing 200,000 pounds were strategically cut with wire-saws and lowered to the ground," he says. Custom-built Hitachi 870 Excavators with a mid-stick boom were used to demolish the superstructure and its 65-foot-tall piers.

By June, the Silverado team successfully demolished two bridge spans of the viaduct and their associated piers over the nine railroad tracks on the east bank side of the river. Silverado was granted a 59-hour work window over three weekends to complete these removals. Geo-fabric, timber mats, 1-inch thick steel plates and 2 feet of rubble were used to protect the railroad tracks from damage during demolition of these spans.

Deconstructing the Signature Spans

The crew returned in late August to remove the East River Pier after the river spans were removed. Just past the mid-way point of the viaduct were two more spans. Constructed of two sets of steel arches anchored into the Center River Pier, each of these signature spans were approximately 160 feet in length and 80 feet above the river channel floor.

"In this section, crews demolished the concrete deck, then cut and lowered the arches and structural steel framing. One of the four arches was saved and is being incorporated into the new construction project," Ngo notes.

After removal of the two river spans, crews demolished the two concrete spans over the remaining nine railroad tracks on the west bank. Silverado worked with SSW and the railroad agencies including Amtrak, BNSF Railway, Metrolink, MTA and the Union Pacific Railroad, to secure a 56-hour work window to complete this segment during three weekends in October. "Every work window granted was completed safely and ahead of the allotted time," he says.

Beyond the demolition aspect of the project, there was a solid recycling component, with over 5,400 cubic yards of asphalt and 4,000 tons of steel recycled. The viaduct demolition was finished in early November, with removal of the last 800 feet of superstructure, the west abutment and a portion of the gateway tunnel. Punch-list and cleanup followed, with final project completion in December 2016. Fortunately, Silverado performed the viaduct demolition safely and with no injuries. According to the project partners, the Sixth Street Viaduct Replacement Project is the largest bridge project in the history of Los Angeles.

Filling Equipment Needs

Bejac Corporation provided the equipment for the project, including Link-Belt 350, 470, and 800 excavators with Atlas Copco hammers. These units were used in the demolition of the bridge and helped keep the job on schedule. "Bejac has a large inventory of specialty demolition equipment to help contractors like Silverado meet the demands of the challenging work they perform," says Vice President and General Manager Robert Cycon. Founded in 1953, Bejac has seven locations across California and Arizona, serving a number of industries, including demolition, recycling, construction and forestry.

According to Cycon, "Bejac has a long history of partnering with Silverado. Some of these projects include the Oakland Bay Bridge, Candlestick Park in San Francisco, and Power Plant projects in San Diego and Bakersfield." For the Sixth Street Bridge project, Bejac kept four mechanics on-site in a 24/7 rotation to perform needed service and maintenance on equipment during critical phases of the demolition and to help ensure the project would be completed on time. "Bejac provides timely service and offers top-of-the-line equipment," Ngo comments. Since opening their Southern California office in 2011, Silverado has utilized the services of Bejac for both servicing equipment and heavy equipment rental.

Agency Partnerships

"This project was challenging for all, with numerous agencies involved in the administration aspect," Ngo states. This included three different departments of the City of Los Angeles, Caltrans, the Federal Highway Administration, five different railroad agencies, as well as the U.S. Army Corps of Engineers, Water Quality Board and U.S. Department of Fish and Wildlife. "With the help of SSW, numerous meetings were held with applicable parties to develop, review and coordinate the work," he says, crediting both teamwork and communication to Silverado's completion of the project safely and within the allotted contract time.

"We have the proven ability, resources and commitment to deliver any challenge safely, on time and within budget," says Ngo. "Our satisfied clients will attest to our excellence and professionalism." Silverado will return for Phase Two of the Sixth Street Bridge project in 2019 to remove a portion of the gateway ramp and tunnel.